Major advantages over PHP4 version:
* Most of the package's functionality is covered by unit tests
* DOM-like API for building the form structure, new streamlined API for
elements' values handling
* Default rendering without tables (inspired by
HTML_QuickForm_Renderer_Tableless)
* Renderer plugins for elements with complex rendering needs
* Ability to chain validation rules with 'and' and 'or'
* Client-side validation can run "live" on changing the form fields,
validation errors are displayed near the fields instead of in alert()